Considerable evidence indicates that T cells are important in the pathogenesis of rheumatoid arthritis. The major goals of our current studies are to characterize the T cell receptors (TCRs) expressed by clonal CD4+ T cell expansions in the synovial fluid of patients with rheumatoid arthritis and to determine the specificity of these clones. The TCRs expressed by these clonal expansions are expressed in T cell hybridomas in order to determine the specificity of these T cells for synovial antigens. In addition, we have been using covalent class II MHC-collagen peptide and cartilage glycoprotein peptide complexes and tetramers to stain for specific T cells in synovium and blood of patients. Despite marked heterogeneity of the synovial T cell receptor sequences, we noted that 20-30% of the TCRB sequences found in one joint were also expressed in a second joint but not in peripheral blood T cells of the same individual. Analysis of TCRB complementarity determining region 3 (CDR3) sequences showed the presence of large clonal expansions present in two or more joints. Continued analysis of the TCR beta-chain and beta-chain repertoire showed remarkable homology among clones within an individual patient, strongly suggesting selection by the same synovial antigen. Together, these studies suggest that a significant proportion of synovial CD4+ T cells have been selected and expanded by conventional antigens in this disease. In the recent funding period, hybridomas expressing RA synovial TCRs have been generated, and we have been screening for responses to candidate synovial antigens and peptides. No responses to synovial antigens have been found. However, we have expanded CD4+ synovial T cells that appear to react to Epstein-Barr virus antigens and possibly hepatitis C antigens. HLA DR4-collagen type II covalent complexes and tetramers have been produced and verified to stain hybridomas specific for the correct peptide (CII p259-271) presented by DR4. Studies examining synovial fluid and stimulated blood and synovial fluid samples from patients and controls are in progress.